Stained my new fiberglass door and put first coat of polyurethane on it and now it has bubbles. How do I remove the bubbles?

I started to paint my kitchen with my husband and let him take over while I went to work and after it had dried the red walls were different colors. I want to know if I need to start over and paint the walls again with a primer and then

We are painting a barn, classic red with white trim. I think we should use a primer tinted half way to the red in order to get good coverage. Now what about the white trim x’s on the doors? What is the best way to mask/paint those without getting the